Enhancing The Performance And Stability Of Perovskite Solar Cells With Different Structures

Hybrid organic-inorganic perovskite has been intensively studied around the world in recent years because of its excellent photovoltaic property and low material cost.The efficiency of perovskite solar cells(PSCs)have risen from 3.8%to 22.1%within 7 years.The instability of PSCs under illumination(including ultraviolet light)is the main barrier to achieve practical applicationIn this paper,four type PSCs with different structures were prepared through spin-coating based on anti-solvent one step method.Several methods,such as interface engineering and doping,were applied in improving the performance of PSCs.The stability of devices based on different structures was measured under 1-sun illumination and UV light,respectively.The causes of failure and associated mechanisms of device degradation were discussed,meanwhile,the strategies about improving the stability of PSCs were proposed in this paper.The main contents are in the following:(1)The PSCs with a structure of FTO/c-TiO2/mp-TiO2/MAPbI3/Spiro-OMeTAD/Au have been fabricated using three methods including one-step,two-step and anti-solvent one-step spin coating.The device based on anti-solvent one-step shows the best performance among all the devices.Then,the preparation conditions based on anti-solvent one step were optimized,such as dropping time of diethyl ether,heat treatment time,concentration of the precursor solution and humidity in the air(2)Based on the configuration of FTO/NiO/MAPbI3/PCBM/Ag,we propose an interface engineering which can not only effectively increase the performance of devices,but also improve the stability.The fullerene amine interlayer(PCBDAN)in planar PSCs can reduce the interface barrier between ETL(PCBM)and metal electrode(Ag);meanwhile improve the electron extraction efficiency between the ETLs and perovskite.The maximum efficiency of PSC with PCBDAN is 17.2%,much higher than that of devices without PCBDAN.Fathermore,the air stability of PSCs with fullerene amine was improved due to the hydrophobic of PCBDAN,which can protect the perovskite film the damage of moisture in air.(3)Based on the configuration of ITO/PCBM/MAPbI3/Spiro-OMeTAD/Au,the low-temperature processed PSCs with high performance and good UV stability were attained by adding the self-organized PCBDAN into PCBM.The ITO/PCBDAN/PCBM structure can be realized through spin-coating the mix-solution of PCBM:PCBDAN in chlorobenzene.The self-organized interlayer(PCBDAN)can effectively decrease the interface barrier between the electrode and ETL.The resultant N-I-P PSCs can reach an effciency of 18.1%,with almost free hysteresis.Moreover,it is verified that our PSCs exhibit excellent stability under 1-sun illumination and UV light.(4)Based on the configuration of ITO/SnO2/MAPbl3/Spiro-OMeTAD/Au,we provide a novel and effective doping strategy to enhance the performance of perovskite solar cells through adding the graphene quantum dots(GQDs)into SnO2.It has been demonstrated that the photo-generated hot electrons in GQDs can transfer to the conduction band of SnO2.The transferred hot electrons from the GQDs will effectively fill the electron traps,as well as improve the conductivity of SnO2,which is beneficial for improving the electron extraction efficiency and reducing the recombination at the ETLs/perovskite interface.The device fabricated with SnO2:GQDs could reach steady-state power conversion efficiency(PCE)of 20.23%,and the hysteresis could be alleviated effectively.(5)It is proposed that highly photostable perovskite can be attained by using the organic semiconductor as electron transport layer instead of inorganic metal oxide.The stability of PSCs based on different structure was measured under 1-sun illumination and UV light.The results show that the PSCs based on inorganic metal oxide including TiO2,SnO2 and NiO was continuous degeneration under constant illumination,and while that based on organic transport layer(PCBM:PCBDAN)has excellent stability.It is demonstrated that the inorganic metal oxides are strong ultraviolet(UV)photocatalyst for destroying the perovskite on its surface under UV illumination,harmful for the stability of the PSCs.In comparison,the organic electron transport layer without photocatalysis is a good candidate to achieve long-term photostable and efficient PSCs.